Sept. 19, 2011 -- Obesity increases the risk that young children will become socially isolated by their grade-school years, a new study shows.

The study tracked more than 3,300 children in Australia for four years as they advanced from preschool through the early grades.

Families were recruited into the study in 2004 with a follow-up in 2008. At those times, measurements were taken of kids' heights and weights. Primary caregivers were interviewed in detail. Parents and teachers were asked to complete additional questionnaires that took stock of the children's mental health problems and their quality of life.

At 4 and 5 years of age, 13% and 16% of boys and girls, respectively, were classified by their weight and height as being overweight; about 5% of both sexes were obese.

Researchers found that kids who were obese compared to their classmates at ages 4 and 5 were up to 20% more likely to face difficulties in their peer relationships by ages 8 and 9 than normal-weight kids.

Difficulties reported by parents and teachers included teasing and rejection, trouble making friends, and not being included in social activities like birthday parties.

Those relationships remained when researchers adjusted their data to reflect the influence of other things that are known to affect social functioning, like mom's mental health and education, family income, and speaking a foreign language at home.

Researchers also saw no evidence of a chicken-and-egg phenomenon with social isolation and weight. That is, when they looked at children's mental and social functioning at ages 4 and 5, they found no evidence that kids who were showing signs of isolation or loneliness at that age were more likely than kids who were having normal social interactions with their peers to go on to become overweight or obese.

When Size Becomes a Stigma

The finding echoes previous studies in older children and adolescents that have found that those who are overweight and obese are more stigmatized, isolated, and disconnected from social networks than their normal-weight peers.

Study researcher Michael G. Sawyer, MBBS, PhD, professor and head of the Research and Evaluation Unit at the University of Adelaide's Women's and Children's Hospital in Australia, says in an email to WebMD that obesity may hurt children's mental health in a couple of ways.

"First, obese children may consider themselves to be the target of criticism, leading them to withdraw from peer activities," he says. And second, it is possible that adults model critical attitudes and behaviors about body size which are imitated by other kids at school.

Experts who were not involved in the research praised the fact that it followed kids into their school years, when social interactions become important for self-esteem.

They also liked that researchers queried both teachers and parents, who may see different sides of the same child.

"This definitely reinforces what I see on a day-to-day basis in the office," says Roya Samuels, MD, a pediatrician at Cohen Children's Medical Center in New Hyde Park, N.Y. "I see a great deal of young patients who are overweight and obese, and the parents do express frustrations about how sometimes their children, especially at a young, tender age, do often get teased at school and how that plays into their self-perception and self-esteem.

Samuels also liked the study because it focused on the mental difficulties associated with obesity, a topic that sometimes doesn't get as much attention as the physical risks. "It's not just the physical ailments that we're concerned about in children who are overweight and obese, but also their psychosocial development," she says.

Other experts said they wished the researchers had used longer questionnaires to measure mental problems. With shorter tools, like the ones used in the study, other mental problems could have been missed, says Paul Ballas, MD, a Philadelphia-based child psychiatrist and representative of the American Academy of Child and Adolescent Psychiatry.

Ballas also wished researchers had tried to tease out the effects of physical problems the obese kids may have been experiencing and their behavior.

"There's a direct correlation between sleep problems and obesity in children, and the worse a child's sleep is, the worse their emotional health is," he says. "And there might be a direct relationship between sleep and obesity that's causing emotional problems and difficulties with social interactions just from the weight itself, independent of the stigma."

Advice to Parents

"It is very important for their future health that we reduce rates of obesity among young children in our community," Sawyer says.

"My advice to parents would be to work hard to help their children achieve the best quality nutrition standards, participate in activities which have the potential to improve fitness levels, and to seek out activities in the community where children's peer relationships can be fostered and supported," he says.

Ballas says there are some concrete steps parents can take to help their children overcome the stigma of being obese.

"If there's a TV in their bedroom, just get it out," says Ballas. "If there's a TV in their bedroom it substantially increases the chance for obesity and sleep problems, and getting the TV out of the room reduces those chances."

Also encourage exercise, but maybe not competitive sports, which can heighten an overweight or obese child's sense of stigma and failure, according to Ballas. "A lot of kids have a great interest in learning and academics that are not necessarily sports related."

Ballas says parents should nourish a child's interest in group activities like music, academic teams, or drama. "Those are things that can be encouraged that may provide positive social benefits that they may not be able to get from sports."